The overall aim of this project is to describe the mechanism by which the properties of ion channels in the membranes of excitable cells can be modulated by events occurring within the intracellular environment, in both developing and adult cells. The specific experiments of this proposal will be done on starfish oocytes. Immature oocytes are large, amenable to a variety of detailed electrophysiological techniques, and under voltage-clamp display voltage-dependent Ca and K currents similar or those of adult neurons and muscle fibers. My preliminary studies have shown that the properties of both Ca and K currents change dramatically during maturation of the oocytes, the final (1-2 hr.) step of oogenesis during which meiosis is reinitiated and the oocyte becomes fertilizable. These changes in the active electrical properties of the oocyte are required for normal fertilization of the mature egg to occur. Although this preparation provides an ideal opportunity to examine rigorously the mechanisms by which Ca and K channel properties are modified during early development, no previous studies have investigated these mechanisms. I will use voltage-clamp, patch-clamp, and ion--sensitive microelectrode techniques to study the effects of maturation and fertilization on Ca and K channel properties. The goal of these experiments is to understand the cellular events of early development which cause the changes in ion channel properties. The results obtained will be of relevance to pathologies affecting the fertilization process, the early development of the nervous system, and the electrical properties of adult nerve and muscle.